Method for promoting a chemical reaction with radioactive gas



Sept. 29, 1970 TOMOMICHI KAS'AMATSU 3 ,38

METHOD FOR PROMOTING A CHEMICAL REACTION WITH RADIOACTIVE GAS 2 Sheets-Sheet 1 Filed Jan. 28, 1966 INVENTOR.

AGENTS Sept, 29, 1970 TOMOMICHI KASAMATSU 3,531,388

- METHOD FOR PROMOTING A CHEMICAL REACTION WITH RADIOACTIVE GAS Filed Jan. 28, 1966 2 Sheets-Sheet 2 I o c':

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u: -20 Q o O Y i 2 A l I n l A I 3456789|O|ll2 RISE OF SURFACE IN V EN TOR. TOMOMICHI KASAMATSU KM- Kai-M AGENTS United States Patent Office Int. (:1. Bin 1/10 US. Cl. 204-157.1 6 Claims ABSTRACT OF THE DISCLOSURE Chemical reactions in a liquid medium are promoted by bubbling krypton 85 through the medium. The dose rate obtained from the finely dispersed gas is very high. Apparatus for performing the method is disclosed.

This invention relates to a method of promoting a chemical reaction by means of ionizing radiation, to apparatus for performing the method, and particularly to a method and apparatus for promoting a reaction in a liquid reaction medium.

I have found that chemical reactions in a liquid medium can be promoted very efiiciently by passing a radioactive gas through the medium in direct contact therewith, and particularly by circulating the gas through the medium to which it should be inert. When the gas is passed through the medium at a rate suflicient to leave at least a portion of the gas undissolved, voids filled with the gas are formed in the liquid, and the dose rate of radiation applied to the medium can be conveniently controlled by maintaining the void fraction at a predetermined value.

The term void fraction, as employed in this application, will be understood to be the ratio of the volume of the voids to the combined volumes of the liquid medium and the voids, and will normally be expressed in percent.

Noble gases are preferred in the method of the invention because of their general chemical inertness and low solubility in most liquids at ordinary temperatures, and krypton 85 is the most readily available radioactive noble gas isotope. Kr has the additional advantage of producing mainly shortrange ,B-radiation, and only little more penetrating -radiation. It thus requires relatively light shielding only.

The radioactive gas is circulated through the liquid reaction medium in the form of finely dispersed bubbles. The degree of dispersion may be controlled at will so that a practically homogeneous mixture is readily obtained and the energy of radiation of the gas is fully utilized. Relatively small radiation doses are, therefore, required to perform a desired reaction, and reactions heretofore not economically performed by means of radioactive promoting agents thus become practical with the high yields of the instant method.

The gaseous, inert and insoluble or sparingly soluble radioactive gases of the invention are readily separated from the liquid reaction medium which may thus be recovered free from residual radioactivity.

Other features and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments, when considered in connection with the accompanying drawing in which:

FIG. 1 shows apparatus for performing the method of the invention in conventional symbols and partly in elevational section;

FIG. 2 is a diagram of the relationship between radiation dose and void fraction in the reaction vessel of the apparatus shown in FIG. 1; and

3,531,388 Patented Sept. 29, 1970 FIG. 3 diagrammatically illustrates the relationship between void fraction and liquid level in the same vessel.

Referring now to the drawing in detail, and initially to FIG. 1, there is seen a gas tight enclosure 53 of heavy mild steel in which the working elements of the apparatus are enclosed, with the exception of a gas tank 1 for krypton 85 under pressure, a gas tank 2 for compressed nitrogen, a compressor 3 for supplying compressed air to the devices in the enclosure 53, a storage tank 16 for the liquid reaction mixture to be processed, and two centrifugal blowers 20, 21 the function of which will presently become apparent.

A control valve 29 in the enclosure 53 connects the tank 1 with the suction inlet of a rotary vacuum pump 6 capable of producing a vacuum of 5 10 mm. Hg and with a storage and mixing tank 9. The tank 9 is equipped with a pressure gage 26 and is connected to the nitrogen tank 2 by a control valve 39. A valve 40 connects the tank 9 with the intake of a circulating pump 10 which is also connected to the intake of the vacuum pump 6 through a valve 41 and with the gas outlet of a mist separator 14. The discharge conduit of the pump 10 is provided with a needle control valve 45, a pressure gage 28, and a flow meter 24, and leads to a gas dispersing plate 11' of fritted glass arranged near the bottom of a sealed reaction vessel 11 of heat and shock resistant glass having a capacity of 1.8 liters. The inlet of the aforementioned mist separator 14 is connected with the cover of the vessel 11.

A valve 16 in the enclosure 53 connects the storage tank 16 with a measuring vessel 15 equipped with a sight glass 15' Whose calibration marks are not shown in the drawing, and which is connected to the vessel 11 by another valve 47 for gravity flow of liquid from the tank 16 to the vessel 11.

A platform 12' carrying two containers 12, 13 is arranged under the vessel 11, and can be shifted horizontally and vertically by an electric drive arrangement, not illustrated, for immersing the vessel 11 either in the container 12 or the container 13. The container 12 normally contains a refrigerant mixture, and the container 13 is equipped with nonillustrated electric resistance heaters for heating the immersed vessel 11. The sensing units 54, 55 of two Geiger counters, not otherwise shown, are mounted in the gas mixing and storage tank 9 and the reaction vessel 11, respectively.

The discharge line of the vacuum pump 6 is equipped with valves 33, 33' and 48, and leads to a trap 17, normally charged with activated carbon refrigerated by means of liquid nitrogen. The air compressor 3 communicates with the discharge line of the pump 6 between the valves 33 and 33' through a valve 31, and a valve 43 connects the part of the discharge line between the valve 33' and 48 with the discharge conduit of the pump 10.

The intake of the blower 21 is connected to the trap 17 and has a vent open to the atmosphere. The blower 20 draws gas from the enclosure 53 through a trap 18 and is capable of maintaining a pressure of less than 20 mm. water column in the enclosure. The gaseous material withdrawn from the enclosure and the gas discharged from the vacuum pump 6 are diluted with much air from the vent in the intake of the blower 21, and are discharged through a nonillustrated stack by the lastmentioned blower.

It will be understood that the aforementioned valves and pumps arranged Within the enclosure 53 are electrically operated and are remotely controlled in a conventional manner. The valves are generally of the shutoff type, except for the needle valve 45, and the control valves 16', 29, 31, 39, 47 which are motor operated.

The enclosure is equipped with windows of lead glass for observation of the pressure gages 26, 28, the flow meter 24, the sight glass and other control instruments omitted from the drawing for the sake of clarity since they are not essential to the operation of the apparatus under normal conditions, and are conventional in themselves.

All piping, valves, pumps and containers in contact with the reactants and the radioactive gas are made of stainless steel of the 18-8 type and are lead shielded, as needed. The mild steel enclosure 53 is adequate for protection against radiation from strongly diluted krypton 85, but may be further enclosed in a shell of concrete blocks, if needed.

Oil separators and filters, and driers associated with the various pumps in a conventional manner also have been omitted from the drawing, and the illustrated valves are merely those needed for normal operation. Additional valves may be provided for maintenance purposes and for permitting elements of the assembly to be replaced without admitting air to the system.

The aforedescribed apparatus is operated as follows:

The tank 9 and the reaction vessel 11 and associated conduits are first evacuated by means of the pump 6 while the valves 40, 41, are open. The evacuated gas is discharged through the open valves 33, 33, 48, and the trap 17 and the blower 21 in which it is diluted by air.

The liquid to be treated is admitted to the measuring vessel 15 by the valve 16' in the desired amount read from the gage 15, and is then dropped into the reaction vessel 11 through the valve 47. Radioactive gas from the tank 1 and inert diluent from the tank 2 are admitted to the mixing and storage tank 9 until the pressure gage 26 and the Geiger counter 54 indicate that the desired mixture has been produced. The mixed gas is admitted to the circuit of the pump 10 until the pressure gage 28 indicates that the desired gas pressure in the vessel 11 has been reached.

The gas mixture is driven by the pump 10 through the valve 45 and the flow meter 24 into the gas dispersing plate 11 from which it rises in finely dispersed bubbles through the liquid contained in the vessel, is separated from entrained liquid droplets in the mist separator 14, and returns to the intake of the pump 10. The rate of gas circulation is capable of being precisely controlled by means of the needle valve 45 to the desired reading of the flow meter 24.

When the reaction is completed, the radioactive gas mixture is expelled from the liquid in the vessel 11 by shifting the platform 12 until the reaction vessel 11 is immersed in the heating tank 13. The vessel 11 is thereafter immersed in the refrigerant in the tank 12 to reduce the vapor pressure of the liquid medium in the vessel 11, whereupon the gas collected in the vessel above the liquid level is drawn off through the mist separator 14 and the opened valve 41 by the vacuum pump 6, and discharged through the valves 33, 33, and 48, as described above. Heating, cooling and evacuation of the vessel 11 are repeated until the Geiger counter indicates the desired removal of radioactive material. Two or three cycles are normally required.

The entire system is then purged by means of compressed air from the compressor 3 while all valves are open, except for the control valves 29, 39 and the valve 33'. If so desired, the intake of the compressor 3 may be connected to a nitrogen tank, and purging of the system with nitrogen has obvious advantages if several successive batches of liquid are to be processed with a mixture of nitrogen and krypton 85.

Although the other noble gases have radioactive isotopes useful in performing the method of the invention, Kr offers a combination of properties not readily found in other chemically inert radioactive gases. It does not react with other materials under the conditions normally encountered in a system of the type described above and readily separates from water and other solvents in which it is practically insoluble. It does not induce secondary radiation from the reactants, the product of reaction, nor the materials of construction employed in the apparatus. Its half-life is quite long, and it does not require heavy shielding since it produces beta-radiation almost exclusively, only 0.65% of the total radiation being of the gamma type.

Argon 39 may also be used to advantage where its short half-life is not objectionable.

Mixtures of 5% Kr and of an inert diluent carrier gas, such as nitrogen, are handled very conveniently because the gamma radiation emitted from the mixture is very weak. For the purpose of the following discussion, Kr may be considered a beta-emitter only.

The liquid reaction medium in the vessel 11 is exposed to radiation of Kr present in three distinct phases. The major portion of the radioactive material is present in gas bubbles which fill voids in the liquid medium. A very small amount of the krypton is dissolved in the liquid, and a more substantial amount of the gas is contained in the top of the vessel as a continuous phase above the liquid level, but has relatively little effect on the liquid.

The radiation received by the liquid from the gas bubbles is a function of the void fraction, as defined above. The radiation received from dissolved krypton is a function of temperature and follows Henrys law. The volume of gas above the liquid level and the amount of radiation received therefrom by the liquid are inversely related to the void fraction.

The relationship between void fraction and the total dose rate from Kr in all three phases has been calculated and confirmed experimentally to be as shown in FIG. 2 when the vessel 11 is charged with 1000 ml. of liquid medium. Since the liquid level in the vessel 11 rises in the vessel 11 as bubbles of gas are dispersed in the liquid, the rise of liquid level in the vessel is a direct measure of void fraction, as shown by the chart of FIG. 3. FIGS. 2 and 3 jointly provide an indication of the total dose rate from a reading of the liquid level in the vessel 11.

The dose rate thus is readily controlled by variation of the circulation rate of the radioactive gas mixture which causes corresponding variations in the void fraction, and the flow meter 24 may be directly calibrated in dose rate for any known mixture of Kr and nitrogen or other inactive diluent. Variations of dose rate greater than those available by manipulation of the needle valve 45 may be achieved by varying the composition of the gas mixture in the storage and mixing tank 9.

When 1000 ml. water are placed in the reaction vessel 11 and a mixture of 5% Kr and 95% nitrogen equivalent to 200 Curie is circulated through the reaction vessel 11 by the pump 10 at such a rate that the void fraction is 40% and the pressure in the vessel 11 is 0.9 atmosphere, the radiation dose rate in the vessel 11 is 3.0 10 rad/hr.

Higher dose rates, of course, are available by raising the concentration of K1' and mixtures containing 50% Kr are readily handled in the apparatus shown in FIG. 1. Heavy lead shielding on all containers and conduits and an outer shell of concrete blocks over the enclosure 53 are required under such operating conditions.

The following example is further illustrative of the method of the invention, as performed in the afore-described apparatus, but it will be understood that the invention is not limited to the example.

EXAMPLE After completion of the reaction, the vessel 11 was im mersed in a mixture of Dry Ice and methanol in the container 12 so that the liquid in the vessel was frozen. The gas collected above the aqueous material was returned to the tank 9 by the pump 6 through the open valves 41, 34. The vessel 11 was then heated in the container 13, and cooled again below the freezing point of its contents, and the gas was removed. The procedure Was repeated a third time, and ultimately the liquid in the vessel 11 was purged with pure nitrogen drawn from the tank 2 through open valves 39, 40 and the pump 10, until the Geiger counter 55 indicated the absence of radiation. The krypton bearing nitrogen was drawn off by the vacuum pump 6 and discharged into the atmosphere by the blower 21.

The contents of the vessel 11 were removed and analyzed for ferric ions present. The radiation dose was calculated from the analysis result as 1.8 X 10 rad.

A second run was made with 500 ml. of the ferrous sulfate solution, a krypton/ nitrogen mixture of /95, and a void fraction of 40%. In a third run, 500 ml. of the same solution were treated with a mixture of 2.5% Kr and 97.5% nitrogen at a void fracture of 25%.

The radiation dose calculated from the void fraction and that determined experimentally by chemical analysis showed close agreement:

Third run-.. 1.0)( rad 1.1X10 rad.

Other reactions capable of being promoted by ionizing radiation can be performed in the same apparatus in an analogous manner, and other radioactive gases and diluents may be employed in an obvious manner.

The method of bubbling a radioactive gas through a liquid reaction medium in continuous stream is far more effective than the use of Co or Cs as sources of gamma-radiation, or that of Sr as a source of beta-radiation since these solid materials must be confined in boxes or capsules, and their radiation can be emanated only through a thin film window.

As partly indicated above, many modifications and variations of the present invention are possible in the light of the above teachings.

What is claimed is:

1. A method of promoting a reaction in a liquid reaction medium, which comprises passing a radioactive gas through said medium in direct contact therewith at a rate sufficient to keep a portion of said gas undissolved, the gas being inert to said medium, whereby voids filled with said gas are formed in said liquid, and controlling the dose rate of radiation received by said medium from said gas by maintaining the ratio of the volume of said voids to the combined volume of said liquid medium and of said voids at a substantially fixed value.

2. A method as set forth in claim 1, wherein said gas is krypton 85.

3. A method as set forth in claim 2, wherein said krypton is diluted with a gaseous carrier free from radioactivity and substantially insoluble in said medium, the amount of said carrier being substantially greater than that of said krypton 85.

4. A method as set forth in claim 1, wherein said gas is circulated through said medium, the gas being intro duced into a bottom portion of said medium, Withdrawn from a top portion, and again introduced into said bottom portion.

5. A method as set forth in claim 1, in which said gas is finely dispersed in bubbles in said medium during said passing.

6. A method as set forth in claim 1, wherein said gas is substantially completely removed from said medium after completion of said reaction.

References Cited UNITED STATES PATENTS 3,100,185 8/1963 Ambrose et al. 204-162 2,865,825 12/1958 Jacobowski et al 204163 OTHER REFERENCES Manowitz, Nucleonics, vol. 11, October 1953, No. 10, pp. 18, 19 and 20.

HOWARD S. WILLIAMS, Primary Examiner Us. 01. X.R g04-1s3, 162, 163 

